1. Field of the Invention
The present invention relates to a method of and an apparatus for automatically finishing a workpiece and, more particularly, to a method of and an apparatus for automatically detecting surface defects and finishing a surface by eliminating surface defects on a workpiece. Such a surface may be the painted surface of a vehicle body.
2. Description of Related Art
Automobile manufacturing lines typically include a surface polishing line for automatically polishing a painted or coated vehicle body surface. A surface polishing line of this kind includes a surface defect detecting station for detecting defects on a painted surface of a vehicle body and a water polishing station for polishing the surface defects to remove them from the surface of the vehicle body. An operator typically visually detects defects on a painted surface of a vehicle body and manually inputs data representative of location, grade, etc., of each surface defect into a terminal device of a polishing line control system at the surface defect detecting station. Based on the data concerning the surface defects, a polishing robot or manipulator automatically polishes out the surface defects. Such a method of and an apparatus for polishing out surface defects on a painted surface of a vehicle body is known from, for instance, Japanese Unexamined Patent Publication No. 58-64,517.
Because painted surface defects must be visually detected by an operator and data representative of the painted surface defects must be input into a terminal device of a polishing line control system, the painted surface defect polishing method and apparatus described in the above-mentioned publication is high in labor requirements.
To save labor in polishing and finishing a painted surface of a vehicle body, in Japanese patent application No. 3-93,040, it has been proposed to provide a surface polishing line for automatically polishing and finishing a painted surface of a vehicle body. In such a surface polishing line, a painted surface of a vehicle body is automatically monitored by an electronic image pick-up device provided at the surface defect detecting station. The electronic image pick-up device automatically detects painted surface defects. The image pick-up device scans surface areas into which the whole surface area of the vehicle body is spatially divided so as to provide image signals of each surface area. Based on data representative of a surface defect in the surface area, such as position data, which is obtained by analyzing the image signals through the use of an image processing device, the polishing manipulator automatically polishes out the surface defects.
In order for the polishing manipulator or robot to locate a polishing tool in the exact position of a surface defect, a calculation must be done to find both a direction in and a distance over which the polishing tool should be moved. This calculation is performed based on the coordinates of the surface defect in a specific surface area and a relative position of the polishing tool with respect to a center of the specific surface area scanned by the image pick-up device. Because a calculation of appropriate directions and distances for the polishing tool requires a long time, polishing out of surface defects is slowed down and polishing tool positioning accuracy is decreased.
For speedy positioning of the polishing tool at the locations of surface defects, it is desirable to install the polishing tool as close to the image pick-up device as possible. However, it is difficult to locate the image pick-up device, which is a very precise optical instrument, close to the polishing tool without polluting the image pick-up device with particles produced during polishing.